Building structure with purlin to beam connection

ABSTRACT

A metal frame for a building structure includes a structural beam, such as a truss, and a tubular purlin or trellis attached to the beam. The tubular purlin includes a configured end matably engaging a side of the beam and an attachment tab extending longitudinally from the configured end. The configured end and the attachment tab both are integrally formed from material of the tubular purlin. The structural attachment tab supports the configured end on the structural beam and structurally attaches the tubular purlin to the structural beam. In one form, the tubular purlin includes a wall section that covers an open end of the tubular beam. In another form, the configured end defines an angled recess setting the particular orientation of the beam relative to the purlin. In yet another form, interlock hooks are provided on the attachment tab.

BACKGROUND

The present invention relates to building structures having structural beams and purlins connected between the beams to create a frame, and also relates to building structures having both purlins and trellis.

Tubular purlins are for the most part presently connected to main beams (e.g. trusses) with welded end plates that cover the end of the tubular purlins. The end plates are bent at the top and have an extending flange with holes for receiving bolts to secure the purlins to a main beam or truss. For example, see Porter U.S. Pat. No. 4,275,534. The end plates are pre-formed separate from the tubular purlins and then attached by welding. This takes substantial material, labor, and time, and further results in extra inventory as well as quality and dimensional control concerns. An improvement is desired to reduce the amount of raw material required for manufacture of building structures, to reduce the number of inventoried components, to simplify the manufacturing process, and to improve assembly, dimensional, and quality control.

Most fabrication machinery only cuts in a single plane or cuts best along a single plane. For example, band saws and similar metal-cutting saws cut best and most efficiently when used to make a planar cut completely across an end section of a work piece. While partial depth cuts can be made with saws, it is largely impractical to do so on a production basis for making building and roof beams and purlins, since partial depth cuts are manually intensive and time-consuming to set up, and further are difficult to accurately control in the heavy gauge metals and high-strength steels used in building beams. Aside from the aforementioned problems, it is very difficult to exactly match the end point of a first cut with a second cut coming from another angle. Notably, mis-cuts and poor dimensional control can be a significant problem when manufacturing structural beam components for buildings, since it can result in considerable field problems during construction and also may potentially raise safety concerns. Still further, with traditional high-volume fabrication machinery, there is no easy way to cut at a varied non-linear direction through a tube. In other words, most fabrication machinery is unsatisfactory for cutting configured ends of a structural tubular beam, when the configured end has multiple cut lines that are not in the same plane, and/or where the cuts are non-linear, and/or where the cut defines a cut direction where another wall interferes with positioning the cutting blade.

With recent advances in laser cutting technology, it is economically possible to make irregular shapes at tube ends. However, I have found that there is a lack of beam joint designs that take advantage of this technology. In particular, I have not found beam joints simplified in the manner and method of the present invention, yet having the structural strength, integrity, robustness, and distribution of stress of the present invention, as described below.

Thus, building structures and, in particular, purlin to beam constructions having the aforementioned advantages and solving the aforementioned problems are desired.

SUMMARY OF THE PRESENT INVENTION

In one aspect of the present invention, a metal frame for a building structure includes a structural beam and a tubular purlin attached to the beam. The tubular purlin includes a configured end shaped to mateably engage a side of the beam, and an attachment tab extending longitudinally from the configured end. The configured end and the attachment tab both are integrally formed from material of the tubular purlin. The structural attachment tab supports the configured end on the structural beam and structurally attaches the tubular purlin to the structural beam.

In another aspect of the present invention, a purlin includes a structural tube adapted to form a structural portion of a building. The structural tube has top, bottom, and opposing side walls. At least the top wall extends longitudinally to define an attachment tab. The bottom wall and at least one side wall has end surfaces defining a concavely-shaped recess adapted to fit closely against a beam with the attachment tab engaging a top of the beam. The attachment tab includes at least two apertures for receiving attachment bolts and has sufficient strength to both support the structural tube on the beam and also sufficient strength to retain the structural tube to the beam for stabilizing the beam.

In yet another aspect of the present invention, a method includes steps of providing a structural tube having top, bottom, and opposing side walls. The method further includes cutting the bottom wall and at least one of the side walls to define a configured end with a concave recess shaped to closely engage a side of a beam, and still further includes cutting the walls to leave an integrally-formed structural attachment tab that extends longitudinally over the concave recess. The method also includes positioning a beam in the recess with the attachment tab engaging a top of the beam and further includes attaching the attachment tab to the beam as a purlin.

An aspect of the present invention is to simply let the integral top wall of the tubular purlin extend over a main beam or truss. The extended top wall defines an attachment tab that becomes structural after it is screwed and/or otherwise fastened to the beam.

Another aspect of the present invention is to cut an end of a structural tubular purlin beam into a configured shape that includes a concavely-shaped recess and a structural attachment tab extending from the remaining end of the tubular beam over the recess. The recess is shaped as desired to receive a beam at a particular angle, and the attachment tab is bent as required. The attachment tab has holes therein for mechanical attachment to the beam.

In a narrower aspect, the integral end surfaces of the configured shape are shaped to retain the beam at a non-perpendicular angle relative to the purlin beam.

In a narrower aspect, the end surfaces of the configured shape form a closure panel shaped to cover an open end of a beam truss.

In another aspect of the present invention, a metal frame for a building structure includes a structural beam having a pair of spaced notches, each notch being located at least partially in a top wall of the beam. A tubular purlin has a configured end including a pair of interlock tabs that hookingly engage the pair of spaced notches with the configured end resting on the structural beam. The configured end and interlock tabs are both integrally formed from material of the tubular purlin, such that the structural attachment tab supports the configured end on the structural beam and such that the interlock tabs structurally attach the tubular purlin to the structural beam.

The present structural purlin to beam connections described above are believed to be novel, useful, and unobvious, particularly in association with modern laser cutting technology, because the connecting configured ends are surprisingly and unexpectedly consistent and robust, and can be made in significant volumes with a reduced amount of high cost manual and skilled labor. Further, the cuts of the configured ends can be made at relatively high speed and quickly with low set-up time and cost.

These and other aspects, objects, and features of the present invention will be understood and appreciated by those skilled in the art upon studying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a fragmentary perspective view of a metal frame including two parallel truss beams, and several tubular purlins extending between and connected to the truss beams;

FIG. 2 is a perspective view of the purlin shown in FIG. 1;

FIG. 3 is a perspective view of a first modified purlin similar to FIG. 2 but with attachment tabs and recesses formed at a slight downward angle to a longitudinal direction of the purlin;

FIG. 4 is a perspective view of a second modified purlin similar to FIG. 2, but with a recess and attachment tab extending at a slight lateral angle to a longitudinal direction of the purlin;

FIGS. 5-6 are front and rear perspective views of a purlin modified to include a wall section adapted to cover an open end of a truss beam; and

FIG. 7 is a fragmentary perspective view of a metal frame for a building, the metal frame incorporating the purlin shown in FIGS. 5-6;

FIG. 8 is a perspective view of a building frame having a constant pentagon-shaped cross section, its roof including the purlins and beams of FIGS. 1-7; and

FIG. 9 is a perspective view of a multi-sided geometrically-shaped “round” building frame, its roof including the purlins and beams of FIGS. 1-7;

FIGS. 10-11 are perspective views of another modified purlin-to-beam arrangement, the purlin including hooked attachment tabs;

FIGS. 12-13 are top and side views of the beam of FIG. 10; and

FIGS. 14-16 are top, side, and end views of the purlin of FIG. 10.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A metal frame 20 (FIG. 1) for a building structure includes one or more structural beams 21, and a plurality of tubular purlins 22 attached to the beams 21 to stabilize the beams 21 to form a rigid building structure, such as the illustrated roof frame structure. The tubular purlin 22 includes configured ends 23 forming a concave recess 23′ shaped to mateably engage a side of the beams 21 and further includes an attachment tab 24 extending longitudinally from the configured end 23 to a distance equal to about half of a width of the beam 21. The configured end 23 and the attachment tab 24 both are integrally formed from material of the tubular purlin 22, as described below. The structural attachment tab 24 forms an arm that supports the configured end 23 on the structural beam 21 and structurally attaches the tubular purlin 22 to the structural beam 24 via a plurality of threaded screws 25 (three screws being illustrated).

The purlin 22 (FIG. 2) is a structural tube made from structural steel and has walls sufficiently thick to form the building structure. The illustrated purlin 22 is rectangular in cross section, and has planar top, bottom, and opposing side walls 26-29. The top wall 26 extends beyond the end surfaces 27′-29′ of the bottom and side walls 27-29 to define the attachment tab 24. A plurality of holes 30 (such as the three illustrated) are formed in the attachment tab 24. The configured end 23 includes the end surfaces 27′-29′ and the attachment tab 24. The configured end 23 forms a concavely shaped recess 31 adapted to fit closely against a side of the rectangular beam 21 with the attachment tab 24 forming a structural arm engaging a top surface 32 of the beam. The attachment tab 24 is sufficient in strength to both support the structural tube 22 on the beam 21 and also sufficient strength to retain the structural tube 22 to the beam 21 for stabilizing the beam 21 in the rigid roof structure.

In the following description, similar and identical features, characteristics and components are identified using the same identifying numbers, but with the addition of a letter “A”, “B”, “C”, etc. This is done to reduce redundant discussion.

The purlin 22A (FIG. 3) is similar to purlin 22, but its attachment tab 24A is bent at an angle 34A to the longitudinal direction “Z” defined by the purlin 22A. Further, the end surfaces 27A′-29A′ of the configured end 23A are cut at an angle to define a 90 degree corner with an inner surface of the attachment tab 24A, so that the recess 23A′ is rectangularly shaped. This allows the rectangular beam 21 to be closely engaged by the configured end 23A on the purlin 22A, even though the purlin 22A does not extend perpendicularly to a side of the beam 21. (See FIG. 4.) This arrangement improves its structural stability after assembly, because the end of the purlin closely engages the side of the beam, despite the non-perpendicularity of the arrangement.

The recesses 23′ and 23A′ are both rectangularly shaped for closely mateably engaging a side of the beam 21, but the end surfaces 27A-29A′ of purlin 22A form a configured end 23A formed so that rectangular recess 23A′ is “rotated forwardly” about an axis “X”. It also is conceived that the end surfaces 27B′-29B′ on purlin 22B (FIG. 4) can be formed so that the configured end 23B defines a recess 23B′ that is rotated about an axis “Y”. (See FIG. 4.) It is further contemplated that a “rectangularly-shaped” recess can be formed at a rotated position that is a combination of rotation about axes “X” and “Y” . . . with the attachment tab being bent as needed to be consistent with and maintain the rectangular shape of the recess.

A purlin 22C (FIGS. 5-6) adapted for use along an eave if a building structure includes walls 26C-29C, with end surfaces 27C′-28C′ cut short to form the attachment tab 24C. However, the side wall 29C has its end surface 29C′ cut in alignment with the end of the attachment tab 24C to thus form a cover tab 34C. The cover tab 34C includes an edge connected to an adjacent edge of the attachment tab 24C. Notably, the recess 23C′ formed by the end surfaces 27C′-28C′ and attachment tab 24C extends at a lateral angle. (Compare to the recess 23B′ discussed above in regard to the recess in purlin 22B.) The cover tab 34C is shaped to cover half of an open end 35C of the beam 21C when the purlin 22C is used along an eave (FIG. 7). Since the recess 23C′ extends at an angle and thus engages the beam at a non-perpendicular position, it is useful along an outer edge of a geometrically “circular” building structure, as shown in FIG. 9, as discussed below.

Many different rigid metal frames for building structures can be constructed by using the above concepts, as will be recognized by persons skilled in this art. Advantageously, the metal frames can be constructed by bolted assembly of beams and purlins, without the need for welding of secondary components and ends pieces to the purlins. It is contemplated that several of the above concepts concerning the purlins can potentially also be employed on the beams, such as for connection of secondary beams to main peak beams, depending on the functional load requirements of the beams.

The building structure 50 (FIG. 8) includes a roof frame structure 51 supported by columns 52. The building structure 50 is elongated to form a rectangular shape when viewed from above, and has a constant cross section forming a pentagon shape when viewed from one end of the building structure 50. The roof frame structure 51 comprises a rigid matrix of interconnected beams 53-55 and purlins 57-58. The illustrated beams 53-55 are relatively consistent in their rectangular shape, and similar to beam 21 . . . though they can be varied in size and strength as appropriate to match particular load and functional requirements. The illustrated purlins 57-58 in FIG. 8 are also relatively consistent in their rectangular shape, and have configured ends using one or more of the concepts discussed above in regard to the configured ends 23, 23A, 23B, and 23C. The purlins 57-58 can also be varied in size and strength as appropriate to match particular beams and to match their design load and functional requirements.

Specifically, in regard to the roof frame structure 51 (FIG. 8), several pairs of opposing angled beams 53 are connected together to a peak beam 54 to form a peak and opposingly angled pitched roof sections. The angled beams 53 are supported near their outer ends by columns 52, with an end section 60 hanging outward from the associated column 52. Another beam 55 is attached between the angled beams 53 and spans between adjacent columns 52. The beams 53-55 may be interconnected by traditional means or by using concepts for configured ends as noted above.

The purlin 57 is connected between the angled beams 53, at an intermediate location between the peak beam 54 and the column-spanning beams 55, with the intermediate purlin 57 extending parallel the peak beam 54. The purlin 57 is a right angle purlin, and has two configured ends 61 similar in shape to the configured end 23 discussed above. An eave-forming purlin 58 is connected between ends of the angled beams 53. The eave-forming purlin 58 is also a right angle purlin and has a configured end 62 similar to the configured end 23 discussed above. However, the configured end 62 has a cover tab (34E) covering half of the open end of the associated angled beam 53.

The building structure 70 (FIG. 9) includes a roof frame structure 71 supported by columns 72. The building structure 70 forms a geometric “circular” shape with flat side sections when viewed from above, and has a repeated roof truss 73 forming a stepped shape when viewed from a side of the truss. Each truss 73 includes a lower angled beam 74, a vertical step beam 75, and a higher angled beam 76. A center point peak structure 77 interconnects the inner ends of the higher angled beams 76, and is of traditional construction. A column 72 supports each lower angled beam 74 at a location slightly inboard of its outer end. A plurality of ring-forming beams 78 interconnect the outer end of the lower angled beams 74 and span between the columns 72. A plurality of middle ring-forming beams 79 extend between the inner end of the lower angled beams 74 to form a first ring around the lower end of the step beams 75, and a second plurality of middle ring-forming beams 80 extend between the outer ends of the higher angled beams 76 to form a second ring around the upper end of the step beams 75. As known in the art, the roof frame structure 71 can be completely supported by the columns 72 at its outer edges, and no columns are required near its center area. When rested on the columns 72, the outer ring of beams 78 are in tension; the lower ring of beams 79 are in compression; the higher ring of beams 80 are in tension; and the peak structure 77 is in compression. All of these connections can be made by traditional means known in the art or by using concepts taken from the technology for making the above configured ends.

The illustrate roof structure 71 includes several purlins 82 that have configured ends 83 similar to the configured end 23B described above. The purlins 82 extend between the adjacent lower angled beams 74 and between the adjacent higher angled beams 76. The purlins 82 are cut to an appropriate length so that the adjacent angled beams 74 and 76 fit closely into the recesses formed by the configured ends 83.

At the outer end of the lower angled beams 78 are attached purlins 85. The purlins 85 include a configured end 86 similar in shape to the configured ends 83, but these configured ends 86 include a cover tab 87 covering an outer open end of the lower angled beams 74 like the cover tab 34E described above.

Another metal frame structure 20D (FIGS. 10-11) includes beams 21D secured together by one or more purlins 22D (or trellis), where the purlin 22D includes a configured end 23D shaped to engage mating notches in the beam 21D. Each configured end 23D has an attachment tab 24D forming a concave recess 23′ shaped to matably engage a side of the beam 21D. A pattern of four notches 91D are cut into the top wall 126D of the beam 21D, two notches 91D on each side. The notches 91D are cut a predetermined distance D1 downwardly partially into a top of the side walls 128D and 129D, and have a lateral spacing of distance D2. The walls 126D-129D have a material thickness of D3. The configured end 23D of the purlin 22D includes a pair of hook-shaped interlock tabs 92D that extend below the attachment tab 24D. The interlock tabs 92D are formed integrally from the material of the side walls 28D and 29D of the purlin 22D. One (or more) holes 93D are formed in the attachment tab 24D at a location aligned with a hole 94D on the top wall 126D of the beam 21D between the associated notches 91D. The interlock tabs 92D are configured to fit downwardly into a pair of the notches 91D on one side of the beam 21D, with the end surfaces 27D′-29D′ of the walls 27D-29D of the purlin 22D engaging the side wall 128D of the beam 21D. The interlock tabs 92D have a hook portion 95D that fits into the purlin 22D and fits closely against an inside of the purlin's side wall 28D. The interlock tabs 92D further have a side stem portion 96D that fits into the vertical portion 97D of the notches 91D (i.e. that portion of the notch located in the purlin's side wall 28D). The side stem portion 96D stabilizes and adds strength to the hook portion 95D and the attachment tab 24D, which may be important depending upon the structural requirements of the configured end 23D in the building structure 20D. A self-tapping screw 98D extends through the hole 93D in the attachment tab 92D of the purlin 22D and threads into the hole 94D in the top wall 12D of the beam. Preferably, the notches 91D are formed with a lead-in angle “A” (FIG. 13) that facilitates entry of the interlock tabs 92D into the notches 91D. Also preferably, the inner side of the interlock tabs 92D have an angled or radiused edge 99D and width 99D′ at a bottom of the notch adjacent the stem portion 96D that facilitates a close fit as the purlin 22D is lowered into position on the beam 21D. The screw 98D assures a tight fit of the purlin 22D onto a top of the beam 21D, which is important for structural reasons and for stress distribution.

Notably, laser cutting technology has now progressed so that the end surfaces 27′-29′ (and 27A′-29A′, 27B′-29B′, etc) and attachment tab 24 (and 24A, and 24B, etc) can be laser cut with precision. Further, laser machinery can be preprogrammed to automatically make a plurality of cuts that are virtually exactly where they need to be with only minimal manufacturing variation. In other words, much tighter tolerances can be held than with traditional cutting processes and machinery requiring individual set-up and cuts. Also, the machines can be programmed to cut a limited depth, such as for cutting only a first side wall while not cutting an adjacent wall and/or not cutting a second side wall that is spaced away only a few inches on an opposite side of the purlin or beam. This allows various purlins and beams to have configured ends accurately and quickly cut by simply calling up the stored data for computer controlled cutting of a configured end. The machine then automatically performs the cuts required. Such machines are commercially available, and need not be described for an understanding of (nor for enablement of) the present invention. The present structural purlin-to-beam connections described above are believed to be novel, useful, and unobvious. They are surprisingly and unexpectedly consistent and robust, and can be made in significant volumes with a reduced amount of high cost manual and skilled labor. Further, the cuts can be made at relatively high speed and quickly with low set-up.

Advantageously, a building structure incorporating a plurality of interconnected beams, purlins, trellises, and/or stabilizers, as illustrated by the beam and purlins, can be quickly constructed to form a secure and stable roof structure, building wall, building overhang, and other structures, with excellent stress distribution and consistent assembly, yet with minimal extra parts and pieces. Installation time and construction materials are minimized. Notably, through use of a high precision laser cutting machine, the joints and configured ends can be accurately and quickly cut, using a database of standardized information and design criteria.

It is to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise. 

1. A metal frame for a building structure comprising: a structural beam; and a tubular purlin with a configured end shaped to mateably engage a side of the beam and an attachment tab extending longitudinally from the configured end, the configured end and the attachment tab both being integrally formed from material of the tubular purlin, the structural attachment tab supporting the configured end on the structural beam and structurally attaching the tubular purlin to the structural beam.
 2. The metal frame defined in claim 1, wherein the attachment tab is formed from a portion of a top wall of the tubular purlin.
 3. The metal frame defined in claim 2, including mechanical fasteners attaching the attachment tab to the structural beam.
 4. The metal frame defined in claim 3, wherein the tubular purlin defines a longitudinal direction and wherein the attachment tab is bent to define an acute angle to the longitudinal direction.
 5. The metal frame defined in claim 4, wherein the configured end includes end surfaces shaped to fit closely to the side of the beam.
 6. The metal frame defined in claim 5, wherein the beam includes an open end, and wherein the configured end includes a first side wall that covers the open end of the beam.
 7. The metal frame defined in claim 6, wherein the configured end includes a second side wall opposite the first side wall, the second side wall being cut short so that a portion of the end surfaces on the second side wall form a notch for receiving the beam.
 8. The metal frame defined in claim 7, wherein the structural beam is oriented at a first angle to horizontal to form a roof pitch, and wherein the purlin is oriented at a second angle to the beam when viewed from above to form part of a geometrically-shaped roof edge, the first and second angles each being less than 90 degrees, the configured end and attachment tab being oriented and configured to nestingly inter-engage.
 9. The metal frame defined in claim 1, including mechanical fasteners attaching the attachment tab to the structural beam.
 10. The metal frame defined in claim 1, wherein the tubular purlin defines a longitudinal direction and wherein the attachment tab is bent to define an acute angle to the longitudinal direction.
 11. The metal frame defined in claim 1, wherein the configured end includes end surfaces shaped to fit closely against the side of the beam.
 12. The metal frame defined in claim 1, wherein the beam includes an open end, and wherein the configured end includes a first side wall that at least partially covers the open end of the beam.
 13. The metal frame defined in claim 1, wherein the configured end includes first and second side walls, the second side wall being cut short so that a portion of the end surfaces on the second side wall form a notch for receiving the beam.
 14. The metal frame defined in claim 1, wherein the structural beam is oriented at a first angle to horizontal to form a roof pitch, and wherein the purlin is oriented at a second angle to the beam when viewed from above to form part of a geometrically-shaped roof edge, the first and second angles each being less than 90 degrees, the configured end and the attachment tab being oriented and configured to nestingly inter-engage an outer end of the beam.
 15. The metal frame defined in claim 1, including a second purlin with a second configured end and second attachment tab, the first-mentioned and second configured ends engaging opposing sides of the beam in a same location, with the first-mentioned and second attachment tabs both engaging a top of the beam in adjacent aligned coplanar positions.
 16. The metal frame defined in claim 1, including at least two screws securing the attachment tab to the beam.
 17. The metal frame defined in claim 1, wherein the purlin includes a second end having a second configured end that is a mirror image of the first-mentioned configured end.
 18. The metal frame defined in claim 1, wherein the beam and the purlin each have flat-sided top and bottom walls.
 19. The metal frame defined in claim 1, wherein the configured end includes end surfaces that are cut at angle that is not perpendicular to the longitudinal direction, so that when the configured end receives the beam, the beam is oriented at an angle less than 90 degrees when the beam and purlin are viewed from above.
 20. The metal frame defined in claim 1, including interlock tabs extending from the attachment tab and that engage a pair of spaced notches in a top wall of the structural beam.
 21. A purlin comprising: a structural tube adapted to form a structural portion of a building, the structural tube having top, bottom, and opposing side walls, at least the top wall extending longitudinally to define an attachment tab; the bottom wall and at least one side wall having end surfaces defining a concavely shaped recess adapted to fit closely against a beam with the attachment tab engaging a top of the beam; the attachment tab including at least two apertures for receiving attachment bolts and having sufficient strength to both support the structural tube on the beam and also sufficient strength to retain the structural tube to the beam for stabilizing the beam.
 22. The purlin defined in claim 21, wherein the top, bottom and opposing side walls are each planar.
 23. The purlin defined in claim 22, wherein the concavely-shaped recess defines a cavity shaped adapted to nestingly engage a beam with a length direction of the beam being at an angle different than 90° to a length direction of the purlin.
 24. The purlin defined in claim 22, wherein the concavely-shaped recess has a cross section with adjacent flat sides adapted to nestingly engage a beam having adjacent perpendicular flat side walls, the flat sides of the recess defining an acute angle to a length direction defined by the purlin.
 25. A metal frame for a building structure comprising: a structural beam having a pair of spaced notches, each notch being located at least partially in a top wall of the beam; and a tubular purlin having a configured end including a pair of interlock tabs that hookingly engage the pair of spaced notches with the configured end resting on the structural beam, the configured end and interlock tabs both being integrally formed from material of the tubular purlin, the structural attachment tab supporting the configured end on the structural beam with the interlock tabs structurally attaching the tubular purlin to the structural beam.
 26. A purlin comprising: a structural tube adapted to form a structural portion of a building, the structural tube having top, bottom, and opposing side walls, at least the top wall extending longitudinally from an end of the structural tube to define an attachment tab with a pair of downwardly extending interlock tabs; the bottom wall and at least one side wall having co-planar end surfaces adapted to fit closely against a building beam with the attachment tab engaging a top of the beam and the interlock tabs engaging mating notches in the beam.
 27. A method comprising steps of: providing a structural tube having top, bottom, and opposing side walls; cutting the bottom wall and at least one of the side walls to define a configured end with a concave recess shaped to closely engage a side of a beam, the step of cutting further including cutting the walls to leave an integrally-formed structural attachment tab that extends longitudinally over the concave recess; and positioning a beam in the recess with the attachment tab engaging a top of the beam and further attaching the attachment tab to the beam as a purlin to form a building structure.
 28. The method defined in claim 27, wherein the step of cutting includes laser cutting the bottom wall and the at least one side wall. 